1. Field of the Invention
The invention is generally related to networking equipment and services. More particularly, the invention is related to design and operation of edge routers that support high speed interfaces.
2. Related Art
Packet switching communications networks are viewed logically as having core networks, edge networks and subscriber/access networks. One protocol for transmission of data over such networks is the IP (Internet Protocol) standard. The edge network aggregates the packet traffic received from subscriber/access networks and forwards such traffic to the core networks. The edge networks serve as an interface between subscribers and the core networks, which are the backbone networks that function over long distances such as those networks administered by major telecommunications carriers. Edge networks often contain “routers” which are devices that determine what network path particular packets should take going forward given their intended destination, state of the network, packet size etc. An example of an edge router is shown in FIG. 1. The edge router 100 contains a number of different sub-systems which carry out the various router functions.
In edge routers that require the support of high-speed physical interfaces, such routers should be so designed such that they are capable of supporting the same speeds through out all the sub-systems in the router. Consequently, this puts a requirement on the switch sub-system 120 within the edge router 100, for instance, to support switching ports at the same higher speeds. The edge router 100 is shown having the following subsystems:                Line Card sub-systems 110, 112, 114 and 116;        System controller Card sub-system 132;        Service Processing Card sub-system 134; and        Switch Fabric sub-system 120.        
Data grams or data traffic (packets or ATM cells that are reassembled into packets inside the line card subsystems) enters the router 100 through physical ports attached to each Line Card sub-system 110, 112, 114 and 116. Each line card sub-system 110, 112, 114 and 116 consists of at least one primary line card and may consist of other associated components such as daughtercards. Depending on the processing needs, each data gram traverses to other sub-systems, such as other Line Cards sub-systems or Service Processing Card sub-systems before going out of the edge router through a physical port attached to another Line Card. A physical port and line card where the data enters the router 100 are respectively referred to as a router ingress port and an ingress line card. Similarly, a physical port and line card where the data leaves the router 100 are respectively referred to as an router egress port and an egress line card.
The Switch Fabric sub-system 120 provides the connecting path between all the other sub-systems in the router 100. Data packets enter the Switch Fabric sub-system 120 from the Line cards or Service Processing Cards through internal ports called fabric ports which are connected therebetween. Ports where the traffic enter the Switch Fabric sub-system 120 are referred to as ingress fabric ports while ports over which the packets leave the sub-system 120 are referred to as egress fabric ports (“egress fabric ports”). Depending upon the destination sub-system, the Switch Fabric sub-system 120 will switch a packet onto an outgoing egress switch port. A switch fabric sub-system 120 will have at least one ingress switch port and one egress switch port for every type of line card or service processing card whose traffic it will switch to other sub-systems.
Thus, referring again to FIG. 1, the line cards of line card sub-system 112 and line card sub-system 114 are ingress line cards while the line cards of line card sub-system 110 and line card sub-system 116 are egress line cards. The same line card can be ingress or egress with respect to a traffic stream depending upon whether that particular traffic stream is entering or leaving the line card sub system. Ingress line cards accept data traffic over router ingress ports and forward traffic therefrom over ingress fabric ports which ingress to the switch fabric sub-system. Egress line cards accept data traffic from the egress fabric ports and forwards it out of the router over router egress ports.
In order to design a system that supports high-speed interfaces such as OC48c (an optical transport standard providing a transfer rate of up to approximately 2.5 Gigabits/second) and OC192 (an optical transport standard providing a transfer rate of up to approximately 10 Gigabits/second), each of the sub-systems in turn must support handling of packets at the same rate. For the Switch Fabric sub-system 120 to switch traffic at such speeds, each of the ingress and egress fabric ports must also be capable of handling packets at the same rate. Problems with the availability of electrical/electronic components (which comprise the network device sub-systems such as line card sub-system) that support high-speed switch ports and the prohibitiveness of the cost of the resulting design are important in design of such routers and network devices. Some possible solutions to these problems include the use of multiple low speed switch (fabric) ports as a substitute for a single high-speed fabric port. For example, multiple lower speed fabric ports, each of which supports OC12c rate (approximately 622 Megabits/second), can replace a single fabric port that would need to support OC48c or OC192c rates. This approach requires load balancing of traffic from the Line cards and service processing cards and other network sub-systems onto the multiple low speed fabric ports. The load balancing solution must take into consideration that the order of packets belonging to a unique IP source and IP destination must be is maintained with in the system. In a switching sub-system, packet ordering is only maintained for traffic originating from a single fabric port. Thus, the load balancing solution must ensure that packet ordering is maintained when traffic is divided onto multiple ports.
It would be desirable to have a router/network device design load balancing solution that addresses the support of a high-speed physical router port/interface with lower speed ports in router/network device sub-systems such as line cards and service processing cards while still maintaining packet ordering.